Well Casing

Four jobs in one pipe: hold the hole open, seal contamination out, protect the pump, and anchor the wellhead.

Well casing is the pipe - steel or PVC in nearly all modern wells - that lines the borehole from the surface down. It is easy to think of the well as "the hole," but in loose soil a raw borehole would slump shut in hours. The casing is what makes the hole permanent.

• Structure: it keeps soil, sand, and gravel from collapsing into the well, for the life of the well.
• Sanitation: together with the grout seal around it and the well cap on top, casing blocks surface water, shallow contaminated groundwater, insects, and debris from reaching your drinking water.
• Protection: the pump, drop pipe, and wiring all live inside the casing, shielded from the formation.
• Structure at the top: the casing carries the sanitary cap and the pitless adapter - the below-frost-line fitting that routes water to your house.

For how the casing fits into the rest of the system - screen, pump, pressure tank - see how a well works and the full well components guide.

The right material is mostly decided by your geology and water chemistry - not by preference.

Regional convention is strong here. In much of New England and other bedrock country, steel casing driven to rock is the standard. In parts of the South and Midwest with deep sand aquifers or corrosive groundwater, PVC dominates. State well codes specify approved materials, wall thicknesses, and joint methods - your state well guide covers the local rules, and a licensed local driller will know the convention cold.

Casing depth follows the geology; casing height follows the code.

In a bedrock well, the casing's job is to get you cleanly through the loose material on top. It runs through the soil and overburden and is seated firmly into solid rock; below that, the borehole is typically left open, because the rock holds its own shape. A 300-foot bedrock well might carry only 40 or 60 feet of casing.

In a sand-and-gravel well, there is no self-supporting rock, so the casing runs essentially the full depth and ends in a well screen - a slotted section that admits water while holding the formation back.

Minimum casing depths, materials, and seating requirements are set state by state in the well code. What is nearly universal is the rule at the top: casing should terminate at least 12 inches above finished grade, higher in flood-prone spots, so runoff can never pond over the top of your well. Wells that terminate in below-grade pits are a legacy design most states no longer allow for new construction.

Your well's original casing depth, diameter, and material are usually recorded on its construction log - look up your well record if you have never seen yours, or explore logged wells around you on the well map.

Casing without grout is a pipe in a leaky hole.

When a well is drilled, the borehole is slightly larger than the casing. That ring of space - the annulus - is a ready-made channel for surface water to run straight down the outside of the casing into your aquifer. Proper construction fills it with grout (neat cement or bentonite clay) from the bottom of the casing up to the surface.

A good grout seal is invisible and permanent; a missing or failed one is a common culprit behind wells that keep testing positive for bacteria no matter how many times they are shock chlorinated. It is also why "my neighbor's well is fine" proves little - sanitation is well-by-well construction, not just the aquifer.

If you suspect the casing or seal, let the water testify before anyone digs: a bacteria and nitrate lab test (kits in our water test store) showing surface-water signatures is the classic fingerprint of a breached casing or failed grout seal.

Water symptoms overlap heavily with pump problems - before assuming the worst, walk through the pump troubleshooting guide. A contractor confirms casing damage with a downhole camera inspection, which also tells you exactly where the damage sits - the single most important fact for pricing the repair.

Most casing problems are fixed with a liner, not a new well - but the honest comparison is worth doing.

• Casing liner (sleeve): a smaller-diameter casing run down inside the existing one and sealed across the damaged zone. The standard fix for cracks, corrosion holes, and joint failures. Trade-off: the well's inside diameter shrinks, which can constrain future pump choices.
• Top-section replacement or extension: shallow damage near the surface can be excavated and the upper casing replaced, or a too-low casing extended above grade.
• Screen repair or replacement: in screened wells, a failed screen (sand pumping) is its own repair path.
• New well: when damage is extensive, deep, or the well is old and undersized anyway, drilling new can beat a stack of repairs. Price both before deciding - see the cost to drill a well.